Venezuela says it is investigating whether a top Colombian rebel leader was seized on its territory.
Rodrigo Granda was dubbed Farc's "foreign minister"
Colombian police said they captured Rodrigo Granda, a senior member of the Farc guerrilla group, in the Colombian border town of Cucuta in December.
But the Farc say he was abducted in the Venezuelan capital, Caracas, with help of Venezuelan and US officials.
The much-heralded capture of Mr Granda looks set to turn into an international incident, says a BBC correspondent.
Venezuela's Interior Minister Jesse Chacon said he had ordered an investigation after confirming that a kidnapping was reported in Caracas on 13 December.
"The investigations still have not shown the identity of the person kidnapped," he told a press conference.
But he said it coincided with a forum organised by left-leaning groups, although it was not clear whether Mr Granda, dubbed Farc's "foreign minister", attended.
"There was a large number of people who participated in this forum who were not invited, both Venezuelans and those from other Latin American countries," he said.
Colombian police announced amid great fanfare in December that they had captured Mr Granda.
His arrest was important because "he was responsible for a campaign of disinformation that hurt the international reputation of Colombia over the last 10 years", National Police Chief Jorge Daniel Castro told reporters.
Mr Granda had visited 16 countries over the past decade trying to build support for the rebels from friendly governments and organisations, he added.
But after his arrest, Mr Granda disputed Colombian police claims that he was arrested in Cucuta and said he had in fact been kidnapped in Venezuela and later moved across the border.
Venezuela's President, Hugo Chavez, has long been accused by Colombia's security forces of sympathising with Marxist rebels.
Whether this is true or not, he will not take kindly to Colombian security forces operating secretly on his territory, says BBC correspondent Jeremy McDermott.
But although the incident may sour already tense relations between the two nations, it is unlikely to get Mr Granda out of jail, our correspondent adds.